Capacitor – Capacitors with Same Voltage, Capacitance, Temp, Different Diameter?

Some cap vendors make their own parts. Some buy caps from a smaller manufacture with the reels re-branded at the fab. Watch out. I got into a mlcc failure investigation in 2002 and started inspecting caps on a reel under a microscope. 3/10 came off the reel cracked. A crack will sooner or later lead to a short. Cracks are not obvious even under a microscope. They may present as a subtle colour shift if the crack is below the surface layer. Some cracks may be sufficient to present a short immediately. Not all. The vendor's manufacturer in this case eventually identified a hopper where the caps were getting cracked.

MLCC are very sensitive to mechanical stress. Especially bigger than 1210 sizes. I found a big power bypass cap adjacent to a heavy mechanical connector once. The nearest mounting hole was 2" away! They were cracking at a rate of 5/10 during install of the unit. A fraction of those were catching fire. The fire would continue to burn until it melted the copper, breaking the power connection.

Another effect of a crack is a reduction of the max working voltage of the cap. It might be spec'd for 200 V. But once cracked it may break down at 40 V. Cracked caps burst into flames in my lab when tested - even below their rated voltage.

Another way to warm up caps is exceeding their max ac current. It's easy to think of caps as zero power dissipation devices. Especially the higher Q mlcc. But they're not. Calculate the power dissipated in caps and do not exceed power/ac current limits. Shows up in power circuits and converters commonly.

1. Having a bunch of caps in parallel will add their capacitance but also puts all their internal resistances in parallel, giving you less overall internal resistance and more current dumping capability.
2. Capacitors don't hold voltage, they hold charge. You can take a set amount of charge and discharge it in a certain time period. You need to rethink of your problem in terms of energy you need and discharge rate of that energy.
3. Caps have a maximum rated voltage above which they'll be damaged. However caps store charge, not just a certain "voltage". They hold energy. 20 uF capacitor can be charged with a 3V rail, or a 6V rail or any rail up to it's maximum rated value. You put a certain amount of charge into it and get a certain amount of charge out of it. The useful thing here is that caps don't like the voltage across them to change quickly. They exhibit inertia when it comes to voltage whereas inductors exhibit inertia when it comes to current. When you discharge a cap you are draining power out of it very quickly. You are dumping out a lot of "energy"/"power". Since P = IV will always be true and caps don't like sudden change of voltage across them they will instead dump a lot of current -- i.e. show sudden change in current to keep the V part of that equation dropping smoothly (or following a discharge curve).
4. A cap's current capability is determined by it's internal resistance + resistance of the load.